It is known to prepare polyurethanes by reacting a prepolymer having isocyanate groups with chain extenders. As a rule products having high molecular weights and high melting points are obtained. Although low-melting polyurethanes are known, the strength properties of such polymers including their tensile strength, percent elongation properties and tear propagation resistance, are poor. However, polyurethanes suitable for use as adhesives for ironing-in materials, as coatings employed in the manufacture of artificial leather, or as protective coatings for materials of any kind, are preferably low-melting polyurethanes having good strength properties.